Peroxisomes from liver and kidney of rat, pig, and dog are being isolated by isopycnic sucrose density gradient centrifugation, and then examined for enzymatic composition besides catalase. Alpha hydroxy acid oxidase in peroxisomes has a different substrate specificity depending upon tissue and animal. NAD-glycerol phosphate dehydrogenase has been found in peroxisomes of both liver and kidney of all animals tested in contrast to the previous idea that this dehydrogenase was solely in the cytoplasm. The transferases for acetyl carnitine and octanyl carnitine were found in liver peroxisomes but not in kidney peroxisomes. These various differences suggest that the enzymatic content of peroxisomes from each tissue of the body must eventually be characterized.